Currently, woven or knitted fabrics comprising low thickness polyester fibers having a thickness of 1 dtex or less and various textile products produced from the polyester fibers are becoming widely used due to the soft and suede-like hand thereof. Also, polyester false twist-textured filament yarns produced by false twist-texturing the above-mentioned low thickness polyester filaments are becoming widely used as materials for interior and interior finish and seats of automobiles, due to not only a soft hand but also a high warm-keeping property, water-absorption and moisture-absorption of the fabrics made from the false twist-textured yarns. The low thickness polyester fibers as mentioned above are difficult to produce and therefore various improvements on the fiber-producing process have been provided in, for example, Japanese Patent No. 3,043,414.
In the conventional melt-spinning process of a polyester polymer, however, a phenomenon occurs such that a foreign matter is generated, adhered and accumulated around the melt-extruding holes of a melt spinneret, with the lapse of the melt-spinning time, the accumulated foreign matter hinders the normal flow of the extruded melt to cause the filamentary streams of the extruded melt to bend, swing or whirl (which may be referred to as irregular extrude phenomena hereinafter), and then finally, the filamentary streams of the extruded melt comes into contact with the accumulated foreign matter and then are broken. The above-mentioned foreign matter may be referred to as a spinneret foreign matter.
Particularly, when polyester fibers having a small individual fiber thickness of 1 dtex or less are produced by a melt-spinning procedure and then taken up, the spinneret foreign matter imparts a serious influence on the extrusion conditions of the polymer melt and within a short time, the irregular extrusion phenomena occur to cause the generation of fluffs on the fibers, the breakage of the fibers to be promoted and the continuous proceeding of the melt-spinning to become difficult. Also, the above-mentioned irregular phenomena cause, in the step of cooling and solidifying of the filamentary streams of the polymer melt, the filamentary polymer melt streams to get an uneven fibrous structure, the resultant polyester fibers thus also having an uneven inner structure. Thus, when the resultant fiber yarn is subjected to a draw and false twist texturing procedure, the uneven inner structure causes the generation of fluffs and the breakages of the yarn to frequently occur.
It is known that the generation and accumulation of the spinneret foreign matter are derived from antimony remaining in the polyester polymer. The antimony is derived from a polycondensation catalyst for the production of the polyester polymer. The antimony-containing catalyst has an excellent polycondensation-promoting property for the production of polyesters, particularly polyethylene terephthalate polymer and the resultant polyester fibers have a good color tone, and therefore, the antimony-containing catalyst is currently most widely employed in practice and thus antimony is widely contained in the conventional polyester fibers.
Alternately, as a polycondensation catalyst for the polyester polymers other than the antimony compounds, titanium compounds, for example, titanium butoxide, are known. When the titanium compound is used, a problem occurs such that the resultant polyester polymer has a yellowish color tone and thus the resultant polyester fibers are not appropriate to use for cloths due to the yellowish color tone, while the generation and accumulation of the foreign matter around the spinneret are decreased.